Broadcasting and telecommunications have historically occupied separate fields. In the past, broadcasting was largely an “over-the-air” medium while wired media carried telecommunications. That distinction may no longer apply as both broadcasting and telecommunications may be delivered over either wired or wireless media. Present development may adapt broadcasting to mobility services. One limitation has been that broadcasting may often require high bit rate data transmission at rates higher than could be supported by existing mobile communications networks. However, with emerging developments in wireless communications technology, even this obstacle may be overcome.
Terrestrial television and radio broadcast networks have made use of high power transmitters covering broad service areas, which enable one-way distribution of content to user equipment such as televisions and radios. By contrast, wireless telecommunications networks have made use of low power transmitters, which have covered relatively small areas known as “cells”. Unlike broadcast networks, wireless networks may be adapted to provide two-way interactive services between users of user equipment such as telephones and computer equipment.
The introduction of cellular communications systems in the late 1970's and early 1980's represented a significant advance in mobile communications. The networks of this period may be commonly known as first generation, or “1G” systems. These systems were based upon analog, circuit-switching technology, the most prominent of these systems may have been the advanced mobile phone system (AMPS). Second generation, or “2G” systems ushered improvements in performance over 1G systems and introduced digital technology to mobile communications. Exemplary 2G systems include the global system for mobile communications (GSM), digital AMPS (D-AMPS), and code division multiple access (CDMA). Many of these systems have been designed according to the paradigm of the traditional telephony architecture, often focused on circuit-switched services, voice traffic, and supported data transfer rates up to 14.4 kbits/s. Higher data rates were achieved through the deployment of “2.5G” networks, many of which were adapted to existing 2G network infrastructures. The 2.5G networks began the introduction of packet-switching technology in wireless networks. However, it is the evolution of third generation, or “3G” technology that may introduce fully packet-switched networks, which support high-speed data communications.
Standards for digital television terrestrial broadcasting (DTTB) have evolved around the world with different systems being adopted in different regions. The three leading DTTB systems are, the advanced standards technical committee (ATSC) system, the digital video broadcast terrestrial (DVB-T) system, and the integrated service digital broadcasting terrestrial (ISDB-T) system. The ATSC system has largely been adopted in North America, South America, Taiwan, and South Korea. This system adapts trellis coding and 8-level vestigial sideband (8-VSB) modulation. The DVB-T system has largely been adopted in Europe, the Middle East, Australia, as well as parts of Africa and parts of Asia. The DVB-T system adapts coded orthogonal frequency division multiplexing (COFDM). The OFDM spread spectrum technique may be utilized to distribute information over many carriers that are spaced apart at specified frequencies. The OFDM technique may also be referred to as multi-carrier or discrete multi-tone modulation. The spacing between carriers may prevent the demodulators in a radio receiver from seeing frequencies other than their corresponding frequency. This technique may result in spectral efficiency and lower multi-path distortion, for example. The ISDB-T system has been adopted in Japan and adapts bandwidth segmented transmission orthogonal frequency division multiplexing (BST-OFDM). The various DTTB systems may differ in important aspects; some systems employ a 6 MHz channel separation, while others may employ 7 MHz or 8 MHz channel separations.
While 3G systems are evolving to provide integrated voice, multimedia, and data services to mobile user equipment, there may be compelling reasons for adapting DTTB systems for this purpose. One of the more notable reasons may be the high data rates that may be supported in DTTB systems. For example, DVB-T may support data rates of 15 Mbits/s in an 8 MHz channel in a wide area SFN. There are also significant challenges in deploying broadcast services to mobile user equipment. Because of form factor constraints, many handheld portable devices, for example, may require that PCB area be minimized and that services consume minimum power to extend battery life to a level that may be acceptable to users. Another consideration is the Doppler effect in moving user equipment, which may cause inter-symbol interference in received signals. Among the three major DTTB systems, ISDB-T was originally designed to support broadcast services to mobile user equipment. While DVB-T may not have been originally designed to support mobility broadcast services, a number of adaptations have been made to provide support for mobile broadcast capability. The adaptation of DVB-T to mobile broadcasting is commonly known as DVB handheld (DVB-H). The broadcasting frequencies for Europe are in UHF (bands IV/V) and in the US, the 1670-1675 MHz band that has been allocated for DVB-H operation. Additional spectrum is expected to be allocated in the L-band world-wide.
To meet requirements for mobile broadcasting the DVB-H specification may support time slicing to reduce power consumption at the user equipment, addition of a 4K mode to enable network operators to make tradeoffs between the advantages of the 2K mode and those of the 8K mode, and an additional level of forward error correction on multi-protocol encapsulated data-forward error correction (MPE-FEC) to make DVB-H transmissions more robust to the challenges presented by mobile reception of signals and to potential limitations in antenna designs for handheld user equipment. DVB-H may also use the DVB-T modulation schemes, like QPSK and 16-quadrature amplitude modulation (16-QAM), which may be more resilient to transmission errors. MPEG audio and video services may be more resilient to error than data, thus additional forward error correction may not be required to meet DTTB service objectives.
While several adaptations have been made to provide support for mobile broadcast capabilities in DVB-T, concerns regarding device size, cost, and/or power requirements still remain significant constraints for the implementation of handheld portable devices enabled for digital video broadcasting operations. For example, a demodulator may be used to accurately recover data from the received signals that may have been down-converted to baseband signals. However, the baseband signals may have unwanted direct current (DC) offsets that may adversely affect the data extracted from the baseband signals.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.